Spore-forming bacteria form a relatively small class of bacteria which are capable of producing endospores. Endospores are dormant non-reproductive survival forms of the bacteria which are resistant to inhospitable environments such as high temperatures, harmful chemical agents and damage from UV light. These spore-forming bacteria comprise Bacillus, Clostridia and Sporosarcina species as well as one strain of Thermoactinomyces and other less common species of Sporolactobacillus and Oscillospira. During a process of sporulation a class of proteins known as the small acid-soluble spore proteins (SASP) are produced. SASP are acid-soluble and have low molecular weights of between 5 and 11 kDa. SASP are reported to have two main roles within bacterial spores: firstly, they act to protect the spore DNA from damage from UV, heat, depurination and many potentially harmful chemical agents; and secondly, SASP provide a source of free amino acids upon spore germination, without which the newly vegetative cells cannot outgrow.
In Bacillus species there are three types of SASP known as α, β and γ type SASP. The amino acid sequences of a/(3-type SASP are highly conserved both within and between species (˜70% identity and ˜80% similarity, without gaps for Bacillus species). However these proteins show no sequence similarity to any other protein family and do not contain any motifs characteristic of other DNA binding proteins (Setlow, 1988). The α/β-type SASP are closely related immunogenically, have molecular weights of approximately 6.2-7.6 kDa and have a significant percentage of hydrophobic amino acids (up to 30%) (Setlow, 1988). The γ type SASP have a molecular weight of 8-11 kDa, are extremely low in large hydrophobic amino acids (<11%) and have a higher isoelectric points than the α/β type SASP from the same species (Setlow, 1988). In any given organism there are two major SASP of the α/β type, as well as many minor α/β type SASP, each encoded by a unique gene (Setlow, 1988). In contrast, all the organisms which have been examined have only one γ type SASP and its function is quite different to α/β type SASP, being used primarily to supply amino acids for outgrowth (Hackett and Setlow, 1987). A list of all the α/β type SASP which have been sequenced to date are given in Appendix 1, together with their related protein sequences. The extent of conserved amino acid residues between these protein sequences is shown in Appendix 2.
Various studies on SASP have focused on characterising the way in which the α/β type SASP protects DNA from UV damage. In one study (Setlow et al 1991) a gene (sspC) encoding an α/β-type SASP was inserted in a plasmid under the control of an inducible promoter to show that SASP cause DNA of a vegetative cell to assume spore-like characteristics. It was observed that binding of α/β type SASP to E. coli DNA caused an increase in plasmid negative superhelical density suggesting a concommitant change in DNA structure. It is postulated that a change in conformation of DNA from B-like to A-like protects the DNA against UV light.
In the field of medicine, regulation of cell growth is a fundamental concern. Cell growth within the body is subject to strict control; this includes both the cells which comprise the body's tissues and organs as well as commensal bacterial cells such as the skin and gut flora. Uncontrolled growth of microorganisms such as bacteria or fungi can be problematic or life threatening to a patient. Common treatment for bacterial infections in particular, involves the use of conventional antibiotics which may have a broad spectrum of activity (such as penicillin) that usually work by targeting bacterial cell walls. Other classes of antibiotics act by inhibiting protein synthesis in the bacterial cell, although many of these also display varying levels of toxicity to human and other animal cells. Bacteria can readily become resistant to conventional antibiotics and “super resistant” strains are now emerging. Thus there is a clear need for alternatives to currently available antibiotics.
Under certain circumstances normal cells in the body's tissues or organs can adopt aberrant characteristics and undergo uncontrolled growth, leading to the disease cancer, which can be life threatening. Many of the current treatments for cancer involve the use of agents or drugs which have toxic and/or unpleasant side effects. Some cancers also exhibit resistance to drugs or do not respond to other treatment regimes, thus alternative control measures are urgently needed.